1. Field of the Invention
The present invention relates to mobile communication networks, and especially to LTE-A (Long Term Evolution) cellular communications in license-exempt TV White Spaces (TVWS) bands, where non-cellular systems such as WiFi (IEEE 802.11 standard), Zigbee (IEEE 802.15), BlueTooth, and USB wireless systems may co-exist.
2. Description of the Related Art
In mobile communication networks, different frequency bands form a resource tightly governed between different users and applications. The governing institutions include several standardizing organizations and e.g. in the USA, the governing institution is the Federal Communications Commission (FCC). Therefore, specific bands are allocated for third (3G) and fourth generation (4G) cellular wireless networks and for WLAN usage. Also, there are specific frequency bands allocated e.g. for TV broadcasting. Generally it can be considered that for any specified specific mobile communication application, some parts of the spectrum are licensed for it and the rest of the spectrum forms unlicensed bands for the application.
An unlicensed band is basically a shared spectrum where one needs to accept interference from other unknown systems and sources such as in ISM (Industrial, Scientific and Medical) bands. As licensed band operation has been increasingly utilized, portions of the radio spectrum that remain available have become limited. Therefore, operators, service providers, communication device manufacturers, and communication system manufacturers, are all seeking efficient solutions to utilize unlicensed shared bands. Communication on an unlicensed shared band has been generally based on sharing an available radio channel between different communication devices. Different communication devices may utilize a common radio access technology (RAT), but it is also possible that different communication devices utilize different RATs which may have different kinds of limitations and different rules in their operation. In an unlicensed shared band, channel access can be distributed in a manner, where communication devices can be configured to detect a channel, and utilize a channel reservation scheme known to other communication devices in order to reserve a right to access the channel.
A potential and attractive spectrum resource is the TV white space (TVWS) band which generally mean all frequency bands allocated for television broadcast signals but which are locally free in a certain geographical area.
The FCC has defined two concepts for helping to find available channels; a TV band database and a geo-location capability. A TV band database that maintains records of all authorized services in the TV frequency bands, is capable of determining the available channels according to a specific geographic location and it provides lists of available channels to TV Band Devices (TVBD) that have been certified under the FCC's equipment authorization procedures. The geo-location capability is defined for some of the TVBDs. A TVBD with such a capability should be able to determine its geographic coordinates within certain level of accuracy, which can be e.g. ±50 m. The geo-location capability is used with a TV band database to determine the availability of TV channels at a location of the TVBD.
Several types of TVBDs have been defined by FCC based on their characteristics. In the USA, the general frequency range for television use is between 54-698 MHz.
The first type of TVBDs is a fixed device. A fixed TVBD is located at a specified fixed location. The fixed TVBD is able to select a channel from the TV band database. Furthermore, it is able to initiate and operate a network by sending enabling signals to other fixed TVBDs or personal/portable TVBDs. Additionally, it is able to provide a list of available channels to a Mode I personal/portable device (see below) on which the Mode I device may operate, especially a supplemental list of available channels for Mode I devices. Such a supplemental list may contain available TV channels that are adjacent to occupied TV channels, for which the fixed TVBDs cannot operate. For instance, the fixed device may be an access point.
The second type of TVBDs is a Mode I personal/portable device. Such a device does not use any internal geo-location capability or access to a TV band database, so it must obtain a channel list from either a fixed TVBD or from Mode II personal/portable TVBD (see below). This kind of device may work only as a client/slave, but not as a master device.
The third type of TVBDs is a Mode II personal/portable device. A Mode II personal/portable device has similar functions as the fixed TVBD, but it does not need to transmit or receive signals at a specified and fixed place. This kind of TVBD can also be an access point, for instance.
The fourth type of TVBDs is a sensing only device. It is a personal/portable TVBD that uses spectrum sensing for determining a list of available channels. It can use frequency bands 512-608 MHz (in USA, TV channels 21-36) and 614-698 MHz (US TV channels 38-51). It is notable that the spectrum sensing is only defined for personal/portable TVBDs.
The transmission power limits are standardized as follows. For fixed TVBDs, the maximum power delivered to the transmitting (TX) antenna shall not exceed 1 W. For personal/portable TVBDs, the maximum effective isotropic radiated power (EIRP) is 100 mW (20 dBm). If the personal/portable TVBD does not meet the adjacent channel separation requirements (the distance between the TVBD and the TV station is smaller than the minimum distance requirement), the maximum EIRP is set to 40 mW (16 dBm).
The maximum power spectral densities (for any 100 kHz band during any time interval of continuous transmission) for different types of TVBDs are standardized for fixed devices as 12.2 dBm, for personal/portable devices operating adjacent to occupied TV channels as −1.6 dBm, for sensing only devices as −0.8 dBm and for all other personal/portable devices as 2.2 dBm.
IEEE technologies represent an attractive choice for the TVWS due to their listen-before-talk nature to provide an inbuilt Physical Layer (PHY)/Medium Access Control (MAC) level co-existence in the unlicensed spectrum. The IEEE projects like 802.22, 802.11af, 802.19.1 and 1900.4a have undertaken actions to address the White Space issues from different points of view.
Solutions for the deployment of LTE wireless nodes such as macro or micro eNodeB:s (eNBs; LTE base stations), pico eNBs, and Home eNBs in heterogeneous networks using the same spectrum are being investigated in 3GPP Release 10 (RP-100383, “New Work Item Proposal: Enhanced ICIC for non-CA based deployments of heterogeneous networks for LTE”, RAN #47, March 2010). Re-use of Release 8/9 techniques, backward compatibility for Release 8/9 terminals, and minimum impact of physical layer air interface are key drivers.
To prevent licensed spectrum scarcity to become a bottleneck for heterogeneous networks due to inter-node interference, LTE systems could be deployed in TV White Space (TVWS) bands with the licensed band resources being used during the initial setup. In the USA, the FCC has regulated licensed or license-exempt TV bands for the secondary-system applications (i.e. cellular, WiFi, WiMax) on TVBDs.
The following table gives the available TVWS bands in the US (see FCC 10-174, “SECOND MEMORANDUM OPINION AND ORDER”, Sep. 23, 2010). Each TV channel has a 6 MHz bandwidth and it would typically be sufficient for any kind of wireless communication.
Frequency Range(corresponding TVCenterchannel numbers)FrequencyAvailable bandwidth 54-60 MHz (2) 57 MHz 6 MHz 76-88 MHz (5, 6) 82 MHz12 MHz174-216 MHz (7-13)195 MHz42 MHz470-608 MHz (14-36)539 MHz138 MHz 614-698 MHz (38-51)656 MHz84 MHz
Most applications in the TV bands are primary applications in some or all the channels, including TV services, Wireless Medical Telemetry Service (WMTS) and radio astronomy, Private Land Mobile Radio Service (PLMRS) and the Commercial Mobile Radio Service (CMRS), and regional based services. In addition, there are also some existing secondary systems such as wireless microphone (channel 7-46) and unlicensed remote control devices (above channel 4).
In prior art, NICT 11-10-1234 (“Channel list request/response for multiple geo-locations”, IEEE 802.11af, October 2010) proposed conditional access to TVWS for the mode II device to check its location every minute (via GPS or some other way), then check if it locates outside the boundary. If it locates inside the boundary, the device doesn't contact the TVWS database. The boundary is determined from operating geographical areas based on operating channels and indicated in WSM IE (White Space Mapping) for current geo-location (accuracy within ±50 m) using available TVWS channel list WSM1 and vicinity geo-location (accuracy less ±50 m) using available TVWS channel list WSM2. This allows the device to check its position in every 60 seconds based on FCC requirements and to contact the database only if its location is outside the signaled geographical areas. The TVWS database may then need to be queried only every 24 hours.
COGEU (“Cognitive radio systems for efficient sharing of TV white spaces in European context”) has proposed a practical approach for geo-location of TVBDs in geographical area (COGEU, FP7 ICT-2009.1.1, D4.1 Spectrum measurements and anti-interference spectrum database specification, 15 Sep. 2010). They recognized that determining that a geographical area is available for White Space Devices (WSD), radio communication depends on signal strength measured at different locations around a given location and compared to some threshold values to establish that the TVBD location probability corresponds to a 70%, 90% or 95% area cell coverage with cell sizes 100 m×100 m, 200 m×200 m or 500 m×500 m, respectively. A geo-location database would work with such a grid, where the device may inform the database on used localization technology, e.g. GPS, cellular based solution Evolved Observed Time Difference Of Arrival (E-OTDOA) using tri-lateration (based on distances) or network-based cell Identity+Timing Advance (cell ID+TA) using triangulation (based on directions). The database may subsequently use a look-up table to ascertain the correct location accuracy. Interference margin to reduce the coverage of the area may be used based on the accuracy of the geo-location, i.e. there may be a smaller list of available TVWS channels within the geographical area. LTE interference to primary systems has also been extensively analyzed. Initial access to the geo-location database by TVBDs by using existing radio interfaces, such as WiFi, LTE or WiMax, has been briefly mentioned in the COGEU approach.
The European Conference of Postal and Telecommunications Administrations (CEPT) has indicated that the geographic area covered by a geo-location database is represented as pixels which are areas of predetermined dimensions (see CEPT/ECC Draft Report 159: “Technical and operational requirements for the possible operation of cognitive radio systems in the White spaces of the frequency band 470-790 MHz”). Each pixel is associated with a list of available frequencies and other relevant data that are provided to cognitive devices querying the database. The exact dimensions of a pixel may depend on planning decisions made in populating the database. The main purpose of using geo-location database for WSD is to ensure that there is no harmful interference from the WSD to the protected services. This is achieved by sharing minimum amount of information between devices and the database to ensure the correct calculation of available channels. In that sense, the CEPT requirements are more flexible than the FCC fixed requirement for geo-location accuracy of ±50 m.
The problematic issue of the prior art is handled in the following. To help the TVBDs find available channels, the FCC has introduced the following issues. TVWS database is available online by the TVBDs (typically via internet connection) that indicate the available channels as a specific geographic location. TVBD geo-location capability is available using GPS or other adequate positioning methods within required accuracy of ±50 m. This is used with the TVWS database to check the available TV channels at a TVBD's location.
In addition, the FCC has defined the following requirements for TVBD types. Fixed TVBDs are located at a specified fixed location and must access to TV band database at least once a day to verify the channel availability. Their scheduling information has to be updated at least in every 48 hours. Mode II TVBDs have to check their locations at least every 60 seconds (except in the sleep mode, when the device is inactive but not powered off) and access the TVWS database if the location has changed either through a direct connection (e.g. via DSL line) or through an indirect connection (e.g. via fixed TVBD or another Mode II TVBD). Mode I TVBDs must either receive a contact verification signal from Mode II or fixed device or contact a Mode II or fixed device to re-verify/re-establish channel availability in at least once in every 60 s period. Sensing only TVBDs use spectrum sensing to determine a list of available channels. They can use the frequency bands 512-608 MHz (US TV channels 21-36) and 614-698 MHz (US TV channels 38-51). Spectrum sensing is only defined for personal/portable TVBDs.
These mechanisms aim to set up TVBD connections in TVWS channels when not used by the primary systems, but they have the following limitations. Geo-location requirement of ±50 m for Mode II device may be difficult to achieve by practical position methods, e.g. GPS, if locating indoors without good line-of-sight (LOS) to several satellites, or cellular positioning techniques such as OTDOA. In addition, in case the available TVWS channel covers a large area (i.e. radius of >>50 m), accessing the TVWS database could be done on a need basis to reduce White Space Mapping (WSM) signaling only if Mode II device leaves the available TVWS channel coverage. Furthermore, these mechanisms do not apply to secondary systems. Cellular network operators may have cellular database showing their coverage accurately, but they are unlikely to allow any competitors to use them. WiFi database including home WiFi networks is not a likely solution.
There is a need to find a solution that allows, on the one hand, to re-use existing mechanisms (i.e. TVWS database, TVBD geo-location) to check that TVWS channels are not used by any primary systems in efficient way, while on the other hand, it is needed to determine whether available TVWS channels are also free from other secondary-system interference.